The TOTAL WAR series may be worth a look. Give EMPIRE: TOTAL WAR a wide berth, as it is heavily bugged and unreliable. Its more recent sequel, NAPOLEON: TOTAL WAR is more stable. However, it's also more 'realistic' which you may find tedious.

ROME: TOTAL WAR is probably the most well-balanced of the recent TOTAL WAR games, plus it allows you to study your towns in 3D mode as they develop (for some reason the others don't) and you build them up, although you don't decide where to build things in a town, merely just order them to be built and they slot in. I always recommend MEDIEVAL II: TOTAL WAR because of the fantastic free mods you can get for it, starting with THIRD AGE (the Lord of the Rings mod).

STARCRAFT is a must, if you've never played it before. It has what is probably the best single storyline of any RTS ever made (although there is strong competition). It's very old-fashioned looking, but worth a look now because STARCRAFT II is due out in the summer. Most copies of STARCRAFT nowdays come with the expansion, BROOD WAR, included.

The HOMEWORLD TRILOGY (HOMEWORLD, HOMEWORLD: CATACLYSM and HOMEWORLD 2) is also awesome. It's fully 3D, set in space, with combat in all three planes. It has some of the best graphics and music ever used in a series of games, but there is relatively little in the way of base-building or management (although both CATACLYSM and HW2 allow you to improve and upgrade your mothership throughout the game).

COMPANY OF HEROES is excellent, but the storyline is a bit cheesier and the WW2 setting puts some people off. Probably more worth a look if you are thinking of going online with it.

The two GROUND CONTROL games are superb, and feature a twist in that they strip away the base-building elements altogether. You deploy an army to the battlefield and that's it, you have to fight with what you are given (although GC2 does allow in-mission reinforcing later on). The storyline is brilliant and both games, despite being the better part of ten years old, still look great. GC1 is one of the hardest games ever made though and is especially notorious for not allowing in-mission saving. The same company made a much more recent game called WORLD IN CONFLICT (about a Soviet/US war in an alternate 1980s) which is great fun, but slightly less accomplished than the earlier games.